50mm liquid screed UFH with Sunamp as storage

[westcoast]

Hello again,

Looking for some advice, any help would be appreciated!

I am in process of building on west coast Ireland. I only have 170mm of floor space for insulation+screed due to a mistake with large sliding doors installation. No going back now. Prob have to go with a 40-50mm liquid screed and maximise my insulation.


Building facts

• 2 bedroom house, wall U-value 0.15, roof 0.13
• Special care is being taken for air-tightness (all Pro Clima stuff)
• high level of thermal mass (block-on-flat construction with 200mmEWI - no internal insulation) partition walls all block. Around windows and 1st and last course thermal block.
• Approx 100m2 of UFH space heating requirements
• Irish winters do not get that cold, just damp. rarely into negative numbers
• UFH will only be used for 3-4 months of the year
• Solid fuel stove for chilly nights. (Double insulated flue, dedicated air intake)
   

 

I'd like to keep my heating system as simple as possible and Willis heaters have been suggested but as I am constrained to a thin screed my floor will not act as a storage heater (heat would be released too early if using E7).

What do you think of these options?:

1. 9kwh Sunamp + E7 electricity, SA will provide the 'storage' element then just blend valve into UFH manifold, it would be an 'on demand' UFH system rather than a giant storage heater slab.

2. ASHP and buffer tank - requires an additional tank, more complex plumbing, maintenance costs, lifespan of ASHP, higher initial cost, noise.

3. another (expensive) option would be to get a Sunamp compatible with ASHP and start with only E7 use then purchase an ASHP later if running costs too high..



(heating requirements attached)

Heat loss calculator - Ballycummin.xlsx

[JohnMo]

Why not a water cylinder instead of a sunamp?   Cylinder, couple of immersions, 180 litre cylinder heated to 70 and drawn down to 25 is 9.5kWh.

 

A2A heat pump?

 

As you have all block work walls, what about in wall heating, same as UFH but in the walls, the blocks acting as the energy store from a Willis heater?  

 

What are you doing for DHW?

[westcoast]

Thanks for the reply!
 

11 hours ago, JohnMo said:

Why not a water cylinder instead of a sunamp?   Cylinder, couple of immersions, 180 litre cylinder heated to 70 and drawn down to 25 is 9.5kWh.

 

Sunamp has about 4x better energy efficiency in terms of heat loss compared to cylinder, no maintenance, much smaller unit, simple install, no discharge pipework etc..  (3x the price though..)

Maybe A2A is the way to go.. I've heard of lot of negativity about them in general. Will have to research further.

 

 

11 hours ago, JohnMo said:

As you have all block work walls, what about in wall heating, same as UFH but in the walls, the blocks acting as the energy store from a Willis heater?  

Very interesting..
 

11 hours ago, JohnMo said:

What are you doing for DHW?

Another Sunamp powered by solar array + E7

Edited May 3, 2022 by westcoast

[ProDave]

4 minutes ago, westcoast said:

Sunamp has about 4x better energy efficiency in terms of heat loss compared to cylinder, no maintenance, much smaller unit, simple install, no discharge pipework etc..  (3x the price though..)

But when a SA goes wrong?  Some reports of failures. You can't just swap the heating element out when it fails.  What will it cost to repair if it breaks after the guarantee has expired?

 

Compared to a HW cylinder, every plumber under the sun knows how to swap a failed immersion heater for not very much money.

[westcoast]

21 hours ago, ProDave said:

But when a SA goes wrong?  Some reports of failures

Thanks Dave, fair enough, that does sound like the sensible option.. i might be a bit fixated on this technology!

The risk of failure though I might be willing to take as the design is inherently simple e.g. no moving parts or corrosion to worry about. 10 year guarantee @ ~3000 euro.

A recent look at the last page of the Sunamp megathread here looks like the mood seems to shifting in favour of the newer units.
 

[JohnMo]

On 04/05/2022 at 18:35, westcoast said:

Inherently simple e.g. no moving parts or corrosion to worry about. 10 year guarantee @ ~3000 euro.

A recent look at the last page of the Sunamp megathread here looks like the mood seems to shifting in favour of the newer units.
 

Not seen any cylinders with moving parts?  Copper and stainless cylinders lasts for decades.  There is no reason copper should not last a lifetime.

 

The real advantage of sunamp are size compared to normal cylinder, and better heat loss profile.

 

But any cylinder in a cupboard surrounded with accoustic insulation will loose the best part of nothing, especially at heat pump temperatures.

[joe90]

1 hour ago, JohnMo said:

But any cylinder in a cupboard surrounded with accoustic insulation will loose the best part of nothing, especially at heat pump temperatures.

+1. 👍

[westcoast]

On 05/05/2022 at 21:44, JohnMo said:

Not seen any cylinders with moving parts?  Copper and stainless cylinders lasts for decades.  There is no reason copper should not last a lifetime.

 

The real advantage of sunamp are size compared to normal cylinder, and better heat loss profile.

 

But any cylinder in a cupboard surrounded with accoustic insulation will loose the best part of nothing, especially at heat pump temperatures.

So is the general consensus for best value still: heat pump + storage cylinder for space heating?

Edited May 7, 2022 by westcoast

[Nickfromwales]

6 minutes ago, westcoast said:

So is the general consensus for best value still: heat pump + storage cylinder for space heating?

All day long. You can bypass the Sunamp and just fit Willis heaters for direct electrical heating, but then you ar stuck with a ratio of 1:1, whereas with a ASHP you’d be more like 2.5-3:1 so around a third of the cost. Completely dependant on whether or not the HP is matched well to the dwelling, and can run at a reasonable CoP.

[westcoast]

Thing is, I believe the house will need very little space heating, prob a pulse in the morning and a pulse in evening for coldest winter months. Pay-back for ASHP could be quite long time. Wonder if direct electric heating (Willis or otherwise) would actually make sense in my situation.

 

Do ASHP units mind being powered-off for 8-9 months of the year?

 

 

 

[Nickfromwales]

6 hours ago, westcoast said:

Thing is, I believe the house will need very little space heating, prob a pulse in the morning and a pulse in evening for coldest winter months. Pay-back for ASHP could be quite long time. Wonder if direct electric heating (Willis or otherwise) would actually make sense in my situation.

 

Do ASHP units mind being powered-off for 8-9 months of the year?

 

 

 

You’d still be using the ASHP for DHW, via an UVC, would you not?

With such a thin screed there will be a very short “thermal time constant” so you’d be stuck with buying electricity on demand. Expensive option if you don’t have a passive raft / similar to invest cheap heat into and leave it leak into the property, as it’ll be 1:1. 
If you have other plans for DHW, you could still just buy a cheap ASHP for heating and get close to 1:4 or at least 1:3.
With electricity prices rising, I’d not go direct with a thin screed tbh. 

[westcoast]

1 hour ago, Nickfromwales said:

You’d still be using the ASHP for DHW, via an UVC, would you not?

No, solar array + E7 + Sunamp(or cylinder) for DHW

 

 

1 hour ago, Nickfromwales said:

With such a thin screed there will be a very short “thermal time constant” so you’d be stuck with buying electricity on demand.

This is what got me thinking about Sunamp in the first place - i could store E7 energy with minimal loss and inject when needed


 

 

1 hour ago, Nickfromwales said:

you could still just buy a cheap ASHP for heating and get close to 1:4 or at least 1:3.
With electricity prices rising, I’d not go direct with a thin screed tbh. 

Hmm, this is another factor I hadnt really considered. ASHP would protect me more for future energy price-hikes 🤔
 

[PeterW]

1 hour ago, westcoast said:

No, solar array + E7 + Sunamp(or cylinder) for DHW

makes no sense. You can’t “overcharge” a Sunamp - when it is full it is full. With a cylinder you can overheat to max the capacity, taking the UVC to 85°C is easily done using your diverter so why not do that ..? 

[DamonHD]

Why do you believe that a Sunamp wouldn't allow similar overcharge?

 

Rgds

 

Damon

Edited May 9, 2022 by DamonHD

[SteamyTea]

35 minutes ago, DamonHD said:

Why do you believe that a Sunamp wouldn't allow similar overcharge

Because it is a phase change material, the vast majority of the energy is stored at the phase change temperature.

I am not sure, but think that 'over charging' causes the pouches to expand, this can cause damage.

8 hours ago, PeterW said:

With a cylinder you can overheat to max the capacity, taking the UVC to 85°C is easily done

That is more a case of under charging most of the time.

 

11 hours ago, Nickfromwales said:

With such a thin screed there will be a very short “thermal time constant” so you’d be stuck with buying electricity on demand

That would need some numbers.  No point over charging the screen if the inside temperature of the house goes too high, with the inevitable window opening to counteract it.

My house has storage heaters, the small, 1.5 kW (10.5 kWh) one has a mass of about 60 kg.

Edited May 9, 2022 by SteamyTea

[PeterW]

4 hours ago, DamonHD said:

Why do you believe that a Sunamp wouldn't allow similar overcharge?

 

Rgds

 

Damon

The control system cuts off the temperature when the PCM is all liquid - you can’t overheat them and they have numerous overheat stats to stop damage. 

[markocosic]

Most phase change material energy storage "happens" during the phase change.

 

Cooling below that temperature or heating above that temperature has materially less effect.

 

Stupid question time: hl

 

How much thermal mass do you have inside your insulation envelope?

 

Floor AND blocks etc.

 

How does that compare with a bucket of water or phase change goop?

 

How long does it take to change temperature for a given heat loss rate / heat input rate?

 

I suspect instant heating of air +by air to air unit or by a thin screed with low mass) which then transfers heat to the masonry will mean you need nothing clever to feed a thin screed.

 

[westcoast]

14 hours ago, PeterW said:

makes no sense. You can’t “overcharge” a Sunamp - when it is full it is full. With a cylinder you can overheat to max the capacity, taking the UVC to 85°C is easily done using your diverter so why not do that ..? 

sorry, I don't understand this, I'm not looking to 'overcharge" my Sunamp.

 

I plan to use primarily solar energy to heat the Sunamp. If its cloudy or short winter days I will use supplementry E7 electricity to complete the charge for the next day.

[markocosic]

Let's do the maths by 10s. (24 hours is 86,400 seconds, but for quick easy maths let's call it 100,000). 

 

 

Water: 4200 J per kg per degC

Plaster / Wood / Concrete / Mineral Wool: all are about 1000 J per kg per degC

 

 

1 kg of water. (1 litre) 4,200 J per degC. Raising the temperature by 1 degC means 4.2 kW for 1 second. (i.e. boiling a 1 litre kettle from 20-100C means 4.2 kW for 80 seconds, or 2.1 kW for 160 seconds)

 

Try 100 kg of water. 420,000 J per degC. Raising the temperature by 1 degC means 4.2 kW for 100 seconds. 420W for 1,000 seconds. 42W for 10,000 seconds. 4.2W for 100,000 seconds. 

 

Say we actually raise the temperature of 100 kg by 50 degC. Now 215 kW for 100 seconds. 21.5 kW for 1,000 seconds. 2.15 kW for 10,000 seconds. 215W for 100,000 seconds. 

 

 

1 kg of plaster / wood / concrete. 1,000 J per degC. Raising the temperature by 1 degC means 1.0 kW for 1 second.

 

100 kg of plaster / wood / concrete. 100,000 J per degC. Raising the temperature by 1 degC means 1.0 kW for 100 seconds. 100 W for 1,000 seconds. 10W for 10,000 seconds. 1W for 100,000 seconds. 

 

Say there's 5,000 kg of plaster / wood / concrete instead. Now 5,000,000 J per degC. Raising the temperature by 1 degC means 50 kW for 100 seconds. 5 kW for 1,000 seconds. 500W for 10,000 seconds, 50W for 100,000 seconds. 

 

 

 

If there's 20 tonnes of plaster / wood / concrete then a 1 degC shift in temperature (absolutely nothing) is the equivalent to a 50 degC shift in 100 litres of water.

 

You've built from lots of material that all takes about 1000 J per degC to change the temperature. In my view it's utterly pointless installing a bucket of water on a sunamp to store heat. Just dump it into the air and let it soak into the building...

[SteamyTea]

1 hour ago, markocosic said:

How much thermal mass do you have inside your insulation envelope

Non, no one has.

[markocosic]

Pedant 😘

[Nickfromwales]

7 hours ago, DamonHD said:

Why do you believe that a Sunamp wouldn't allow similar overcharge?

 

Rgds

 

Damon

PCM58 is called that for a reason .

With an ASHP you can heat an UVC to 55oC, but the immersion heater can then push you way past that to 85oC for a huge increase in stored heat energy fir the same capacity device. 
SA wins on physical size, UVC wins on not being a single trick pony. 
SA fails by the sheer number of failed units I’ve had to exchange or repair vs UVC’s. 

[Nickfromwales]

7 hours ago, SteamyTea said:

That would need some numbers.  No point over charging the screen if the inside temperature of the house goes too high, with the inevitable window opening to counteract it.

My house has storage heaters, the small, 1.5 kW (10.5 kWh) one has a mass of about 60 kg.

I’m not saying to over heat it, but without a decent amount of ‘thermal heat capacity’ you cannot store heat energy and slowly release it, as you do with your storage heaters.

Getting the whole house and internal ambient materials / surfaces up to the desired temp then becomes an event, rather than a constant. Uneconomical by comparison eg between thin screed over a little bit of insulation vs passive raft.